This invention relates to door operators and, more particularly, to a safety arrangement for such an operator which is sensitive to the door striking an obstruction while being closed.
The use of safety arrangements in conjunction with automatic door operators to prevent the door from continuing to close upon striking an obstruction is generally well known, particularly in the case of garage type doors which move along a track toward and away from a fixed surface. Some of the known arrangements sense the striking of an obstruction in an indirect manner such as, for example, by detecting a change in load on the motor driving the door. Other known arrangements use a more direct approach, such as, for example, by employing a light beam which extends along the door edge, the light beam being broken when the door edge encounters an obstruction. However, in a factory environment, such an arrangement has proven to be disadvantageous in that dirt and debris can interfere with the light beam. Another sensing arrangement which has been proposed includes a pair of conductors which are maintained in spaced apart parallel relationship relative to the door edge until an obstruction is encountered, at which time the conductors are moved into contact with each other. This arrangement also suffers from numerous disadvantages such as, for example, build up of debris and/or corrosion on the conductors which either causes the conductors to contact prematurely or prevents the conductors from making any contact. Also, immersion of the conductors in water can cause a false reading.
It is therefore a primary object of the present invention to provide a safety arrangement for a motor driven door which is sensitive to the door striking an obstruction during its travel.
It is another object of this invention to provide such a safety arrangement which does not suffer from any of the disadvantages enumerated above.